This project will investigate the function of a new mouse gene, called Bop, which lies within 500 nucleotides upstream of the CD8b gene and is expressed in CD8+, but not CD4+, T lymphocytes. Expression of Bop is induced in lymph node cells by concanavalin A. The Bop protein is also abundantly expressed in cardiac and skeletal muscle, although this form of the protein (skm-Bop) differs from the protein expressed in T lymphocytes (t-Bop) at its amino terminus. Based upon the localization of skm-Bop to the sarcomere M-band, the applicant hypothesizes that t-Bop plays a role in alteration of the CTL cytoskeleton following antigenic stimulation. Such alterations might include the redistribution of organelles within the CTL as well as changes in CTL motility and lytic activity. The proposed studies are aimed at determining the role of t-Bop in CTLs. The specific aims include (1) determination of the role of Bop in cell growth and function; (2) determination of the cellular location of t-Bop in CTLs using antibody or green fluorescent protein-tagged t-Bop; and (3) determination of the effect of t-Bop knock-out on CTL generation and immune function.